Among others, direct-converting detectors based on semiconducting materials, such as CdTe, CdZnTe, CdZnTeSe, CdTeSe, CdMnTe, InP, TIBr2, HgI2, are used for the detection of gamma and X-ray radiation, in particular in CT, dual-energy CT, SPECT and PET systems. However, these materials have a large number of crystal defects or impurities which may be electrically active as capture and recombination centers and have an adverse effect on the detection of X-ray radiation, by way of example in the form of image artifacts.
In order to optimize X-ray radiation detection it is known to irradiate the semiconductor used for detection with an additional radiation to produce additional charge carriers. Infrared, ultraviolet or visible radiation by way of example is used as additional radiation. In the previously known X-ray radiation detectors, however, non-transparent or opaque electrodes have been used which are arranged on the side face of the semiconductor facing the additional radiation. This non-transparent electrode also connects the material of the semiconductor to a high voltage source or an electrically conductive connection to the high voltage source. The applied high voltage generates an electric field inside the material of the semiconductor which enables movement of the generated charge carriers with respect to the electrode. However, in a non-transparent electrode, the semiconductor is almost completely shielded from the additional radiation, so no additional charge carriers are generated.
Conventional electrodes also exhibit a significant absorption effect for the X-ray radiation to be detected. Due to the requirement to keep the dose rate of a patient in a CT scanner as low as possible, it is desirable to use an electrode with the lowest possible absorption effect. This applies regardless of whether the detector is irradiated with additional radiation or not in order to optimize the X-ray radiation detection.
A direct-converting X-ray radiation detector is known from printed publication U.S. Pat. No. 7,652,258 B2, in which the polarization effects are to be reduced with the aid of additionally irradiated IR radiation in a transparent intermediate layer.
Reference is also made to printed publication US 2012/0068078 A1 which discloses a radiation detector having a semiconductor made from HgJ2, with electrodes made from palladium, TiW, ITO, SnO2, InO3 or carbon membranes, on which a protection layer of silicone or parylene is formed.
Printed publication U.S. Pat. No. 6,163,030 A also discloses a radiation detector having a semiconductor in which electrodes made from TCO, thin metal layers of Au or Pt, or organic conductors such as polyaniline are used.
Finally, reference is also made to printed publication US 2011/0253886 A1 which describes a direct-converting radiation detector, in which light is coupled into a semiconductor layer with the aid of a light source.